Human peripheral blood lymphocytes were fractionated into either thymic dependent (T) cells or thymic independent (B) cells. Unfractionated cells and T cells were shown to be stimulated by phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM). B cells did not respond to any of these mitogens unless a few T cells were added to the culture. Unfractionated and T cells were capable of proliferating in the presence of Plasmodium falciparum malaria antigens; B cells did not proliferate even when T cells were added to the culture.